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Britannicus's picture

Hi there in response to your question - I have to say I've permanently fixed the pivot points - i find it useful to have them there on so many issues, and you don't have to use them.

If you want to do a temporary solution, you could try using "polymorph" (without which no genuine robot builder will be happy) - this is a hard plastic that turns like putty at about 60 degrees C and liquid at 80 - I find it's quite handy  for sticking things and will come off with a bit of help from my wife's hairdryer.  You can get it on Ebay and it's brilliant for all sorts of things ( I know I sound like an advert but I'm not connected with them jsut really like the product)

I did experiment making a simple bracket for the pivot made out of a strip of thin aluminium, which went under the servo and up each side being secured under the fixing screws. It worked OK but was a bit of a hassle to produce, so I went for the easy option and reached for a tube of araldite and glued it on.

 

Hi Bro,

Last month I bought polymorph on ebay for my new project. I prefer  polymorph more than other , because it can let you make any shape you like .

Ya, araldite is more secured.

Britannicus's picture

Hi there in response to your question - I have to say I've permanently fixed the pivot points - i find it useful to have them there on so many issues, and you don't have to use them.

If you want to do a temporary solution, you could try using "polymorph" (without which no genuine robot builder will be happy) - this is a hard plastic that turns like putty at about 60 degrees C and liquid at 80 - I find it's quite handy  for sticking things and will come off with a bit of help from my wife's hairdryer.  You can get it on Ebay and it's brilliant for all sorts of things ( I know I sound like an advert but I'm not connected with them jsut really like the product)

I did experiment making a simple bracket for the pivot made out of a strip of thin aluminium, which went under the servo and up each side being secured under the fixing screws. It worked OK but was a bit of a hassle to produce, so I went for the easy option and reached for a tube of araldite and glued it on.

 

Britannicus's picture

Hi there - I have to say that I glue my pivot points direct to the servo, I can then either use them or not as I choose. all it means is that you have a small screw sticking out of the back as in the picture.

 

You can use custom made mounts which fit round your servo and essentially do teh same thing, but these cost almost as much as a servo I don't tend to bother. I often tend to buy used servos from Ebay which means I don't worry so much about breaking them so much. You can make your own servo brackets with a bit of effort - take a look at Lynxmotion's site, then make your own - that's what I've done a few times !

http://www.lynxmotion.com/p-635-aluminum-multi-purpose-755hbmg-servo-bracket-two-pack.aspx

Cheers Andrew

Uzimonkey's picture

Besides the smoothness issues, this looks good.  It's a simple design, it doesn't look like any of the pieces are particularly complex.  I like the design of the grabber, looks very easy to build.

It looks like you're using two servos to drive the first joint.  Are these driven individually, or from the same pin?

Thanks!

It drive individually .Since I place two servo motor face each other so, when programming , it need to program the servo in opposite direction.

Ro-Bot-X's picture

I once hacked a servo to rotate the opposite way. All it takes is to switch the side leads of the potentiometer (leave the middle in place) and switch the motor leads. On some servos this is difficult, as the motor is soldered directly to the board, but you can use some solder wick and desolder it, then rotate it 180 degrees to switch the leads. Also, you may need to cut the potentiometer leads if they are soldered directly to the board and replace them with wires. Not an easy job, but it works and it makes things a lot easier in code.

Uzimonkey's picture

That's right, I hadn't thought of that.  It's not clear from your page, do you know where the stutter is coming from?

Sorry , What stutter?

Britannicus's picture

First off - I think this is a really good shot at making an arm with servos and a BS2. If I could offer a couple of suggestions to resolve some of your issues with movement, but I think our project is great !

1/ Have you looked at the parallax user forums - they have real experts who give excellent advice. I've been helped with many BS2 issues through them - if you post your code they might be able to offer advice. Secondly - they would be really impressed if you posted your project there, I find them a big help.

2/ I think you could solve some of your problems with a more stable connection at the elbow joint. if you pivoted the arm from both sides of the servo it would reduce the tendency to "bounce". I had a smilar problem with the legs on my hexapod (see http://letsmakerobots.com/node/26783 ) I posted a simple solution to mount a pivot opposite to the rotor on a miniature servo, but it works even better on a standard servo.

3/ I have a simple design for a gripper with a parallel action if you would like it, but rather like your solution as it is - nice and simple !

4/ by the way you can find the Parallax forum on http://forums.parallax.com/ 

Hope this helps